Forced and unforced variability of twentieth century North American droughts and pluvials

Research on the forcing of drought and pluvial events over North America is dominated by general circulation model experiments that often have operational limitations (e.g., computational expense, ability to simulate relevant processes, etc). We use a statistically based modeling approach to investigate sea surface temperature (SST) forcing of the twentieth century pluvial (1905?C1917) and drought (1932?C1939, 1948?C1957, 1998?C2002) events. A principal component (PC) analysis of Palmer Drought Severity Index (PDSI) from the North American Drought Atlas separates the drought variability into five leading modes accounting for 62% of the underlying variance. Over the full period spanning these events (1900?C2005), the first three PCs significantly correlate with SSTs in the equatorial Pacific (PC 1), North Pacific (PC 2), and North Atlantic (PC 3), with spatial patterns (as defined by the empirical orthogonal functions) consistent with our understanding of North American drought responses to SST forcing. We use a large ensemble statistical modeling approach to determine how successfully we can reproduce these drought/pluvial events using these three modes of variability. Using Pacific forcing only (PCs 1?C2), we are able to reproduce the 1948?C1957 drought and 1905?C1917 pluvial above a 95% random noise threshold in over 90% of the ensemble members; the addition of Atlantic forcing (PCs 1?C2?C3) provides only marginal improvement. For the 1998?C2002 drought, Pacific forcing reproduces the drought above noise in over 65% of the ensemble members, with the addition of Atlantic forcing increasing the number passing to over 80%. The severity of the drought, however, is underestimated in the ensemble median, suggesting this drought intensity can only be achieved through internal variability or other processes. Pacific only forcing does a poor job of reproducing the 1932?C1939 drought pattern in the ensemble median, and less than one third of ensemble members exceed the noise threshold (28%). Inclusion of Atlantic forcing improves the ensemble median drought pattern and nearly doubles the number of ensemble members passing the noise threshold (52%). Even with the inclusion of Atlantic forcing, the intensity of the simulated 1932?C1939 drought is muted, and the drought itself extends too far into the southwest and southern Great Plains. To an even greater extent than the 1998?C2002 drought, these results suggest much of the variance in the 1932?C1939 drought is dependent on processes other than SST forcing. This study highlights the importance of internal noise and non SST processes for hydroclimatic variability over North America, complementing existing research using general circulation models.     

Promoting Geography (or Part of It)—Yet Again!

Geographers in the United States frequently express concern that their discipline's potential contributions to the understanding of contemporary society (including society–nature interrelations) and resolution of some of its major problems are underrecognized and undervalued. Understanding the Changing Planet (National Research Council 2010) is the latest in a series of reports addressed at policymakers, the scientific community, and its funders seeking to rectify that situation. It covers the geographical sciences more generally rather than geography specifically and pays particular attention to society–nature interrelations but does those disciplines something of a disservice with its greater emphasis on the infrastructure for data collection, visualization, and analysis at the expense of explanation and theory. It successfully promotes some aspects of the disciplines but largely ignores other vibrant and important parts. Its long-term impact is uncertain.     

Map-based multicriteria analysis to support interactive land use allocation

This article focuses on the use of map-based multicriteria analysis to develop a negotiation support tool for land use allocation. Spatial multicriteria analysis is used to make explicit trade-offs between objectives and to provide guidance and feedback on the land use changes negotiated by the participants. Digital maps are the means of communication among workshop participants, and an interactive mapping device (the ‘Touch table’) is used as the interface. Participants are informed about the relevant trade-offs on the map and use this information to change the land use maps. The approach is tested during a negotiation session as part of the land use planning process of the Bodegraven polder, a peat meadow area in the Netherlands.     

Trace elements in native gold by solution ICP-MS and their use in mineral exploration: A British Columbia example

An elegantly simple, aqua regia-based, ICP-MS analytical procedure is used to compare the trace element composition of density-separated alluvial native Au from seven stream silt samples with three samples of geographically-associated Au from a prospective ore deposit in central British Columbia. Not all of the alluvial Au could have come from the ore deposit based on present drainage. The silt sample Au, averaging four alluvial grains and totaling 12–250 μg per sample, generally yielded measurable concentrations for V, Fe, Cu, As, Pd, Ag, Sb, Pt and Bi. The bedrock Au samples represent the three dominant rock types in the showing. Their Au trace element compositions largely bracket the alluvial Au. Multidimensional scaling (exploratory statistics) shows that trace elements in the native Au form lithophile, chalcophile and siderophile groupings. This indicates that a small set of geochemical processes formed all the Au in one geologic environment. Previous work shows that Au from individual deposits has distinct assemblages of detectable elements. Given these observations and that detectable elements are the same in both the deposit and alluvial Au, and that concentrations in the former bracket those of the latter, it is concluded that the source of the alluvial Au has probably been identified. Apparently neither mineral inclusions nor weathering impaired fingerprinting of the Au. The simplicity of the approach indicates that this is a useful exploration tool for determining the bedrock source of alluvial Au. The study also shows that silt sample exploration in glaciated terrains must recognize that paleo-ice movement and paleo-stream directions can yield geographic distributions of alluvial Au that cannot be explained by present-day drainage patterns. Thus this simple analytical/exploration technique is potentially very useful to the exploration industry.     

The Cold War and geography’s quantitative revolution: Some messy reflections on Barnes’ geographical underworld

A response to a recent paper by Barnes, arguing that the origins of geography’s quantitative revolution were not as monofocused as he suggests.     

The scale of segregation: ancestral groups in Sydney, 2011

Most studies of urban residential segregation analyse it at a single-scale only, usually the smallest for which relevant census data are available. Following a recent argument that such segregation is multiscalar, this paper reports on multilevel modelling of the segregation of 42 ancestral groups in Sydney, Australia, looking at its intensity at four separate scales in which segregation at each scale is presented nett of its intensity at all higher-level scales. Most groups are more segregated at the macro- and micro-scales than at two intermediate meso-scales, with variations across them reflecting their size, recency of arrival in Australia and cultural differences from the host society. The findings are used as the basis for developing a multiscale appreciation of residential patterning.     

Spatial scale and measuring segregation: illustrated by the formation of Chicago’s ghetto

Few studies of residential segregation in cities have directly addressed the issue of spatial scale, apart from noting that the traditional indices of segregation tend to be larger when calculated for small rather than large spatial units. That observation however ignores Duncan et al.’s (Statistical geography: problems in analyzing areal data. Free Press, Glencoe, 1961) explication that any measure of segregation at a fine-grained scale necessarily incorporates, to an unknown extent, segregation at a larger scale within which the finer-grained units are nested. To avoid that problem, a multi-level modelling perspective is introduced that identifies the intensity of segregation at each scale net of its intensity at any larger scale included in the analysis. It is applied to an analysis of the emergence of Chicago’s Black ghetto over the twentieth century’s first three decades, using data at the ward and ED scales. It shows that across Chicago as a whole segregation was equally as intense at the two scales, with statistically significant increases in that intensity at both scales across the three decades. At the finer scale, however, segregation was much more intense across the EDs within those wards that formed the core of the emerging ghetto than it was in the remainder of the city.